1. Field of the Invention
The present invention relates to a method for treating a fluid mass wherein a mass material is fed to vessel or trough having a mixing device comprising rotatably arranged processing means, wherein at least two of the processing means are caused to rotate in opposite directions and essentially horizontally adjacent to one another. The present invention also relates to a method for treating a couch mass or the like, wherein couch mass and dilution water are caused to fall down into a couch pit comprising a trough and a mixing arrangement. Thus, in more general terms the present invention relates to methods for treating a fluid mass or stock and especially a method for treating a couch mass or the or the like, wherein the mass or stock material is fed to a vessel or trough having a mixing device comprising rotatably arranged processing means. The present invention further relates to a processor arrangement for a fluid mass or stock, said arrangement comprising a vessel or trough for the reception of the respective mass or stock, a processing device such as a mixing arrangment arranged in the vessel and comprising horizontally arranged rotatable cylinder body means provided with spirals, as well as a discharge for treated or processed mass or stock. The cylinder means comprise at least two cylinders arranged for rotation counter each other. The invention further relates to a specific use of the method and the arrangement.
2. Technical Background
In paper manufacturing trimmed strips are cut from a wet web, and additionally wet broke material will be generated at the wire and the press section in connection with a web break. Usually the wet broke material is collected, disintegrated and diluted in a pulper comprising a container with a powerful mixing feature and thereafter it is returned to the process.
For the disintegration to function properly the pulper must comprise a sufficient amount of mass or stock which is maintained under a powerful mixing by the disintegration means of the pulper. During regular processing the amount of stock brought to the pulper corresponds to a minor part of a paper machine""s production. At web breaks, changes of quality and machine stops the amount of stock may temporarily rise to an amount corresponding to the total production capacity of the machine.
In order to achieve a satisfactory mixing and disintegration effect the stock in the pulper must be kept highly diluted and a sufficiently large volume of mass must be kept therein. This leads to a high power demand for the disintegration and mixing.
At a web break the water consumption rises greatly and for this purpose a water reserve must be arranged corresponding to the demand at a typical web break. After the disintegration the wet broke material usually is de-watered in a separate de-watering device for better correspondence with the production consistency and for retrieving the water therefrom.
At production changes, especially at a change of color, there will exist a large amount of wet broke material from the earlier paper quality, which amount cannot be used for the next quality. The wet broke material in circulation in the system will also make the attaining of the new paper quality slower and results in productional losses and change-over broke masses.
In this respect it is also of importance that the pulper can be easily and completely emptied of its contents, which is not the case for typical pulpers.
Many paper machines have a low and narrow wire section which does not provide space for the construction of an appropriate pulper. In this case vaulting and broke stocking problems will arise and the pulper itself can be difficult to maintain and service.
Corresponding problems occur in other productions where a mass or different streams of components should be processed in order to achieve a homogenous mass.
Usually the wet broke mass is diluted to a 2 to 3 percent consistency in a couch pit or wire pulper. Depending on the structure of the paper machine a similar pulper may also be arranged in connection with the press section. Depending on the size of the machine the wire pulper is typically between five and fifty cubic meters and it comprises a powerful mixer which breaks up fibre bundles and pieces of paper. For an effective function the pulper requires a good mixing which, in turn, requires a sufficient dilution. Since the pulper works under varying conditions the dilution usually is over-dimensioned according to the most critical situation.
3. Description of Related Art
Publication No. SE-210862 describes a device for processing a material mass in particulate or suspension form, especially for de-fibration of a cellulose material, in which device at least two band spirals are arranged mutually adjacent in a shell having inlet and outlet openings, said spirals being arranged for spaced intermeshed common rotation. Their spiral surfaces are directed generally radially.
Since the device known from SE-210862 has defined inlet and outlet openings and a mainly unbroken axial path of flow it is unsuitable for processing a broke mass which will fall down over the whole width of a paper machine. The axial spiral surfaces give a processing of the mass in a axial direction, and the mixing of the mass which takes place does so because the band spirals will cut through the mass, which provides only a local turbulence and permits the mass to stagnate within the device. A clearance between the band spirals and said shell has also been provided in order to permit this kind of mixing, and separate screws take care of the feeding of the mass through said outlet.
U.S. Pat. No. 2,797,623 discloses a worm conveyor by which broke mass can be transported out from a paper machine. The worm conveyor comprises a screw in which the broke in a traditional manner is brought along a flute. For this transport to function the spiral surfaces of the screw must be arranged essentially radially. Broke falling into the conveyor will thereby be transported straight through the conveyor without any significant mixing.
Publication No. DE-401033 discloses a mixing and transport arrangement having two intermeshed band spirals. Since they are rotating against each other, the material transported by them will be processed in an alternating manner by one or the other of the spirals and thereby a mixing action will be generated. This mixing action thus comprises the spirals moving through the material to be mixed and simultaneously transporting it forwards. A mixing in this kind of agitator requires an easy flowing material and there is a risk, if the screws fill up, for a standing circulation to be caused, since the material can easily flow through hollow portions in the spirals.
Especially in small old paper machines the agitator in the couch pit has been formed as a spiral, with the idea of its pressing the broke material towards the outlet of the couch pit. These spirals, however, have been inefficient in that they have not ground up the broke and have not provided a sufficient power, and thus the broke has been able to vault and block the outlet.
From the pulper the broke is usually transported via a thickener to the machine""s stock chest where it is mixed with fresh stock. This can be arranged in many ways, depending on the machine""s product and equipment. It is usual to combine the thickening of broke with the recovering of fibers in a disk or drum filter.
At a change of quality the broke can be directed to separate collecting tanks from which it is gradually dosed into the stock. In many cases, especially in the manufacturing of colored paper, the broke generated at a change of quality can no longer be added to the process but will be directed to the waste water treatment where the solid material is recovered for incineration or deposition on a waste dump.
Usually the generated broke will be struck from the wire by high pressure water which simultaneously dilutes the broke. There have, however, been developed methods for mechanically dislocating broke, one method used including feeding it over a guiding roll having a doctor blade. Hereby the desire has been to avoid an unnecessary dilution of the broke. There is, however, the problem that broke of a higher consistency tends to vault, which is accentuated by a more difficult mixing.
The object of the present invention is to provide a method and an arrangement for an efficient continuous homogenization of a mass flow, for example wet broke in a paper machine or another fluid mass comprising more or less solid components which are to be disintegrated and/or mixed into a liquid type fluid.
One object of the invention is to minimize the processed amount of mass, which minimizes the loss of time and material at a change and shutdown of the process.
An object of the invention is also to provide a method for handling for example wet broke of high consistency, due to which the need for diluting water and a subsequent thickening is eliminated.
A further object of the invention is to provide (a vaulting and blocking free handling of, for example, broke, also in narrow spaces.
A further object of the invention is to provide an energy saving method for handling of, for example, wet broke.
One object of the invention is to provide an apparatus capable of treating, for example, wet broke in a small volume and one which permits a simple and complete emptying of the same.
One object of the invention is also to provide an apparatus capable of treating, for example, broke of a high and varying consistency.
One further object of the invention is to provide an apparatus of small dimensions which also in narrow spaces is capable of treating, for example, broke without a risk for vaulting and blocking.
One further object of the invention is to provide an apparatus which under a low energy consumption treats, for example, broke.
According to the invention the set objects are obtained by arranging, in a vessel, a system comprising spiral means operating counter to each other and in an intermeshing fashion in such a manner that the mass at the vessel""s wall will reside in channels formed by said spirals, whereby the mass at the intermesh of said spirals will be pressed into a direction which differs from the traditional directions of transportation for the spirals.
Thus, the method according to the present invention is characterized in that at least two of the corresponding means are brought to rotate in opposite directions and essentially horizontally adjacent to one another so that the mass at the upper surface of the means is conveyed outwards towards the respective opposite side walls of said vessel, whereby the mass is brought, by several spiral elements arranged in an inclined manner at an essentially cylindrical core of the respective processing means, into generally inclined channels delimited by the core, by the walls at respective two adjacent spiral elements, and by the vessel""s wall portions adjacent to the respective spiral element, and further towards a constriction or choke formed by the respective intermeshing spiral elements at adjacent processing means.